Vapor phase ring closure



United States Patent 3,350,409 VAPOR PHASE RING CLOSURE Harold A. Kaufman, Piscataway Township, New Brunswick, Ross A. Kremer, Edison, and Patrick Robert Driscoll, Highland Park, N.J., assignors to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Apr. 2, 1965, Ser. No. 445,242 6 Claims. (Cl. 260332.3)

This invention relates to the formation of cyclic ketones by ring closure. It is formation of cyclic ketones by vapor phase catalytic cyclization of aryl-substituted lower alkanoic acids.

It has been proposed to prepare cyclic ketones by a two-step intramolecular acylation of aryl-substituted lower alkanoic acids, e.g., 4-keto-4,5,6,7-tetrahydrothionaphthene from 4-(2-thienyl) butyric acid or a-tetralone from phenylbutyric acid. The acid is first converted to the correspondkeep in a pure state. Consequently, yields are erratic and reproducibility of results is poor. It has also been proposed niques (Belgian Patent No. 638,684).

It has now been found that aryl-substituted alkanoic acids can be converted into cyclic ketones by 'a method that is relatively simple and economically feasible. It has been discoveredthat aryl-substi-tuted alkanoic acids will readily undergo direct intramolecular acylation in a catalytic process carried out in the vapor phase.

Accordingly it is a broad object of this invention to catalytic vapor phase process for converting 4-(2-thienyl) butyric acid to 4-keto-4,5,6,7-tetrahydrothionaphthene. Other objects and advantages of this invention will become in the art, from the following 3,350,409 Patented Oct. 31, 1967 In general this invention provides a process for converting aryl-substituted lower alkanoic acids to cyclic ketones that comprises contacting, in the vapor phase, an acid having the formula, Ar(CH COOH, wherein AI is an aromatic cyclic (heterocyclic or carbocyclic) radical and n is 24, with a dehydration catalyst.

The aryl-substituted lower alkanoic acid reactant that is converted to a cyclic ketone in the process of this invention has the formula Ar(CH COOH, where Ar is an aromatic cyclic radical and n is an integer, 2, 3, or 4. The term aromatic is used, in this specification and the claims, in its broad sense to include heterocyclic as well as carbocyclic ring. In general, it includes ring compound radicals that are aromatic in nature. Thus, Ar can be an gen. Ordinarily, however, the Ar substituent will be unsubstituted, but if cyclized by the process of this invention are 4-(2-thienyl) butyric acid, 4-(2-furyl) butyric acid, phenylbutyric acid, 3-(2-thienyl)propionic acid, 3-(2-furyl)propionic acid, on naphthylpropionic acid, 4-(2-pyridyl)butyric acid, 5-(2- thienyD-n-pentanoic acid, phenyl-n-pentanoic acid, and 5- 2-furyl) -n-pentanoic acid.

The reaction involved z 02 etc.

The process of this invention is carried out in the vapor phase. Accordingly, the reaction temperature will be at least the boiling point of the aryl-substituted 'alkanoic acid reactant and higher. In general, temperatures of between about 250 C. and about 550 C. are utilizable, depending in part upon the'catalyst used. Temperatures of between about 350 C .and about 475 C. are most effective and The process of this invention can be carried out batch- Wise. It is, however, most feasibly carried out continuously. When using a Solid catalyst,

keto-4,5,6,7-tetrahydrothionaphthene in each run are set forth in the table.

TABLE Charge Rate, ccJmin.

Example Catalyst Contact Temp., 0. Yield, wt. Cat. Vo1., cc. Time, sec. percent 2 N2 TBA 1 AlPOr 13 140 0.35 2 375 100 Ca (PO4)2 15 160 0. 40 2 400 93. 4 P10 (15.5%) on Alundum". 40 140 0.50 4 400 3 99. 2 W0 on A1203. 260 0.70 1 390 78. 6 W03 (95%) on A1 0; 15 527 1.40 0.5 400 75.0 A1 0 15 131 0.36 2.2 307 34. 1 CrgOa (33%) 15 160 0. 40 2 400 38. 8 Montmorillonite 15 160 0. 40 2 400 11. 8

1 4-(2-thienyl)butyric acid. 1 Yield Micro-4,5,6,7-tetrahydrothionaphthene. 3 Added 85% H3P04 at 0.0125 cc./min. to and reaction products through the reactor bed can be facilitated by using an inert sweep or carrier gas, such as nitrogen or flue gas.

The following examples demonstrate the process of this invention is the conversion of 4-(2-thieny1)butyric acid to 4-keto-4,5,6,7-tetrahydrothionaphthene. It must be understood that other aryl-substituted alkanoic acid reactants and catalysts, as set forth hereinbefore, can be employed.

Example 1 The reaction system used comprised a tubular reaction vessel containing a static bed of catalyst and provided with means to heat the catalyst bed. The inlet to the reactor comprised an opening for introducing reactant and a preheater section, and openings for introducing nitrogen carrier gas and liquid catalyst (phosphoric acid). The outlet from the reactor Was provided with a condenser section and a receiver for the reaction product.

The catalyst used in this run was prepared by pouring 90 g. of 85% orthophosphoric acid over 300 g. of alundum balls and heating to dryness with occasional stirring. Heating time was about 2 /2 hours.

The acid reactant, 4-(2-thienyl)butyric acid, was charged in a vapor state to the reactor, containing 142 cc. of the phosphoric acid of alundum catalyst at a temperature of 400 C. The acid reactant was charged at a rate of 1.778 cc. per minute, corresponding to an LHSV of 0.75 (0.0747 min. contact time). Nitrogen carrier gas was fed at the rate of 497 cc. per minute. There were added 6.5 ml. of 85% phosphoric acid during the addition of acid reactant at the rate of 0.016 cc./min. There was a total recovery of 97%, which was found by vapor phase chromatography to contain 95% 4-keto-4,5,6,7-tetr ahydrothionaphthene, 2% unrecated 4-(2-thienyl)butyric acid (recyclable), and 3% byproducts, all by weight. The cyclic ketone product was identified by comparison with a standard, by infrared analysis. It was characterized chemically by converting it to 4-hydroxybenzothiophene.

Examples 2 through 9 A series of runs was carried out for converting 4-(2- thienyl)butyric acid into 4 keto 4,5,6,7-tetrahydrothionaphthene. In each run, a different dehydration catalyst was used. Pertinent process conditions and yields of 4- maintain activity.

It will be noted that the process of this invention converts an aryl-substituted alkanoic acid to the corresponding cyclic ketone in good yield. Various catalysts are efiective, but all are not equally effective. When yields per pass are low, however, recycling unconverted arylsubstituted alkanoic acid will afford good ultimate yields.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

What is claimed is:

1. A process for producing 4-keto-4,5,6,7-tetrahydrobenzothiophene that comprises contacting 4-(2-thienyl) butyric acid, in the vapor phase, with a dehydration catalyst selected from the group consisting of phosphoric acid, sulfuric acid, phosphoric acid on alumina, sulfuric acid on alumina, alumina, phosphorus pentoxide, tungsten oxide, oxides of Th, Ti, Zr and Mo, acid activated montmorillonite, AlPO and Ca (PO 2.. The process defined in claim 1, wherein said dehydration catalyst is orthophosphoric acid.

3. The process defined in claim 1, wherein said dehydration catalyst is aluminum phosphate.

4. The process defined in claim 1, wherein said dehydration catalyst is calcium phosphate.

5. The process defined in claim 1, wherein said dehydration catalyst is phosphorus pentoxide.

6. The process defined in claim 1, wherein said dehydration catalyst is tungsten trioxide.

JOHN D. RANDOLPH, Primary Examiner. WALTER A. MODANCE, Examiner. C. M. SHURKO, Assistant Examiner.

Berichte 56, 620 to 623 

1. A PROCESS FOR PRODUCING 4-KETO-4,5,6,7-TETRAHYDROBENZOTHIOPHENE THAT COMPRISES CONTACTING 4-(2-THIENYL) BUTYRIC ACID, IN THE VAPOR PHASE, WITH A DEHYDRATION CATALYST SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID, SULFURIC ACID, PHOSPHORIC ACID ON ALUMINA, SULFURIC ACID ON ALUMINA, ALUMINA, PHOSPHORUS PENTOXIDE, TUNGSTEN OXIDE, OXIDES OF TH, TI, ZR AND MO, ACID ACTIVATED MONTMORILLONITE, ALPO4, AND CA3(PO4)2. 